Increasing Costs Due to Ocean Acidification Drives Phytoplankton to Be More Heavily Calcified: Optimal Growth Strategy of Coccolithophores

Ocean acidification is potentially one of the greatest threats to marine ecosystems and global carbon cycling. Amongst calcifying organisms, coccolithophores have received special attention because their calcite precipitation plays a significant role in alkalinity flux to the deep ocean (i.e., inorganic carbon pump). Currently, empirical effort is devoted to evaluating the plastic responses to acidification, but evolutionary considerations are missing from this approach. We thus constructed an optimality model to evaluate the evolutionary response of coccolithophorid life history, assuming that their exoskeleton (coccolith) serves to reduce the instantaneous mortality rates. Our model predicted that natural selection favors constructing more heavily calcified exoskeleton in response to increased acidification-driven costs. This counter-intuitive response occurs because the fitness benefit of choosing a better-defended, slower growth strategy in more acidic conditions, outweighs that of accelerating the cell cycle, as this occurs by producing less calcified exoskeleton. Contrary to the widely held belief, the evolutionarily optimized population can precipitate larger amounts of CaCO3 during the bloom in more acidified seawater, depending on parameter values. These findings suggest that ocean acidification may enhance the calcification rates of marine organisms as an adaptive response, possibly accompanied by higher carbon fixation ability. Our theory also provides a compelling explanation for the multispecific fossil time-series record from ∼200 years ago to present, in which mean coccolith size has increased along with rising atmospheric CO2 concentration

Iron Oxydation and Deposition in the Biofilm Coverign Montacuta ferruginosa (Molusca bivalvia)

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Manganese transformations by marine Bacillus species,

ABSTRACT. A wide variety of micro-organisms promote the oxidation or reduction of manganese, through indirect or direct mechanisms. An example of the latter category is Bacillus SGl, a marine organism isolatefJrom a aear-shore manganese sediment. Its mature domwnt spores catalyze the oxidation ofMn to Mn +. The process requires molecular oxygen and is catalyzed by a spore coat component. The manganese oxide (Mn02) produced remains bound to the The vegetative cells do not have the oxidizing capacity. They are able to reduce Mn + to Mn + under low-oxygen conditions. The reducing activity has a pH optimum of 7.5 and is abolished by preheating of the cells at 90° C for 5 minutes. Addition of mercuric chloride (HgC12) (final concentration 0.01%) to cells which are actively reducing manganese oxide causes immediate cessation of the process. Manganese oxide reduction is also inhibited at high oxygen tensions and by inhibitors of the electron transport system. Bacillus cells contain b- and c-type cytochromes which are oxidized in situ when manganese oxide is added to an anoxic cell suspension. The results suggest that vegetative cells may use the manganese oxide formed by the spores from which they germinate as a terminal electron acceptor. The possible applications of manganese transforming micro-organisms in human society are discussed

Response of the calcifying coccolithophore Emiliania huxleyi to low pH/high pCO2: from physiology to molecular level

The emergence of ocean acidification as a significant threat to calcifying organisms in marine ecosystems creates a pressing need to understand the physiological and molecular mechanisms by which calcification is affected by environmental parameters. We report here, for the first time, changes in gene expression induced by variations in pH/pCO2 in the widespread and abundant coccolithophore Emiliania huxleyi. Batch cultures were subjected to increased partial pressure of CO2 (pCO2; i.e. decreased pH), and the changes in expression of four functional gene classes directly or indirectly related to calcification were investigated. Increased pCO2 did not affect the calcification rate and only carbonic anhydrase transcripts exhibited a significant down-regulation. Our observation that elevated pCO2 induces only limited changes in the transcription of several transporters of calcium and bicarbonate gives new significant elements to understand cellular mechanisms underlying the early response of E. huxleyi to CO2-driven ocean acidification